On 02/13/2012 11:46 AM, Paul Zarnowski wrote:

[...] I see the following major categorizations of how to protect
(large) file servers effectively.  Please feel free to comment on
this, as I'm looking to refine my view.

I should say that our "protection goal" would be to have a copy of
 data at our medical college campus, which is ~200+ miles away and
 accessible via a 10Gb WAN.

1. Backup using NDMP: breaks down as data size increases, because of
need for periodic full backups and lack of incremental forever.
However, probably fast recovery times from tape.  Most NAS products
support some version of NDMP.

2. Incremental file-level backup based on Journal Scanning, saving a
 walk of the filesystem.  Examples include Windows-based
 fileservers, and (I think) SONAS.

3. Incremental backup based on Snapshot differencing, again saving a
walk of the filesystem.  This would be NetApp, but not with
MultiStore vFilers - a problem for us.

4. Asynchronous replication to a second NAS.  Fast RTO, but also
expensive.

Options 1-3 use TSM.
Options 2&3 run faster and are more scalable than option 1, but likely have 
longer RTO.
Option 4 is probably most expensive.

I'm going to assume

0. Conventional TSM backup via a proxy node.  Requires keeping shares
quite small (no more than a few TB), if you want anything approaching
daily incrementals.  Bottleneck appears to be metadata scan, walk of
tree.

I mention that because Isilon (and others?) are starting to offer
options that let you keep metadata on SSD, which may change the
maximum size for reasonable conventional incrementals.  We're
expecting to do a POC of Isilon before too long, I intend to examine
that.


-----


As for comment, I want to amplify what you said about RTO: Your option
4 is in a completely different universe from the 0-3.  For all of 0-3,
the DR critical path includes an acquisition cycle.  I'm not sure our
heirarchy could get a PO out in a week if their hair were on
fire... yours may be better.

Option 4 has nearly immediate recovery, in degraded performance.  So,
it's more expensive, but it moves you to a totally different recovery
mode.

Our thinking abount isilon backups includes a remote "Near-line" unit,
that has relatively large, slow, cheap drives.  It would be a
replication target for several other units, giving it good efficiency
of scale.



- Allen S. Rout